1. Field of the Invention
The present invention relates to a magnetoresistive head for use in, for example, a magnetic recording/reproducing device, such as, a magnetic disk unit and a magnetic tape unit.
2. Description of the Prior Art
In the magnetic disk unit, the magnetic tape unit and the like which record and reproduce data, a data recording density has been improved to be higher year after year.
In response to this situation, a magnetoresistive head (hereinafter also referred to as "MR head") has been developed since the MR head is capable of dealing with those data recorded in such a higher density.
On the other hand, in order for the MR head to reproduce an output waveform which precisely corresponds to a magnetic field generated on a magnetic recording medium, it is necessary to operate a magnetoresistive film or layer (hereinafter also referred to as "MR film") in a linear resistance variation region. In order for this, a bias magnetic field should be applied to the MR film.
As one method for applying the bias magnetic field to the MR film, there has been proposed the SAL (soft adjacent layer) bias method which can provide a high bias efficiency with a low current. In the SAL bias method, a for-bias soft magnetic film which is attached to the MR film via a spacer is magnetized by means of a magnetic field generated due to a current flow in the MR film, and a direction of magnetization in the MR film is rotated or angularly changed to be perpendicular to a surface of the MR head confronting the magnetic recording medium (hereinafter also referred to as "medium confronting surface") by means of the magnetized for-bias soft magnetic film.
The effect of the SAL bias method will be described in detail hereinbelow.
FIG. 2 is a graph showing an H-R line representing a relationship between a magnitude of the magnetic field (H) applied or inputted to the MR film as represented by the axis of abscissas and a magnitude of the electric resistance (R) of the MR film as represented by the axis of ordinates. As appreciated from FIG. 2, the electric resistance of the MR film changes depending on a magnitude of the inputted magnetic field. Accordingly, assuming that the inputted magnetic field in FIG. 2 is the magnetic field generated on the surface of the magnetic recording medium, the electric resistance of the MR film changes depending on a condition of the magnetic field on the surface of the magnetic recording medium. Therefore, when a constant current is set to flow in the MR film, the magnetic field recorded on the magnetic recording medium, that is, the recorded magnetic data can be read out by measuring a voltage applied across the MR film. However, as described above, in order to obtain the output waveform which precisely corresponds to the inputted magnetic field, the MR film should be operated in its linear resistance variation region as represented by B in FIG. 2. In FIG. 2, the H-R line is indicated as being shifted leftward by applying the bias magnetic field to the MR film so that the MR film can be operated in the linear resistance variation region B with respect to the inputted magnetic field, meaning that the output waveform which precisely corresponds to the inputted magnetic field, i.e. the recorded magnetic field on the magnetic recording medium can be reproduced. On the other hand, if no bias magnetic field is applied to the MR film, the electric resistance of the MR film is maximum when a magnitude of the inputted magnetic field is substantially 0 (zero), and decreases as a magnitude of the inputted magnetic field increases or decreases from the value 0 (zero). Accordingly, the MR film can not be operated in the linear resistance variation region B with respect to the inputted magnetic field so that the reproduced output waveform differs from the corresponding inputted magnetic field.
FIG. 1 is a partial perspective view showing a conventional MR head.
In FIG. 1, numeral 1 denotes a for-bias soft magnetic film, numeral 2 a nonmagnetic spacer film disposed on the for-bias soft magnetic film 1, numeral 3 an MR film disposed on the nonmagnetic spacer 2, and numeral 4 electrode films for supplying a sense current to the MR film 3. Further, in FIG. 1, alphabet Z represents a direction of an axis of easy magnetization of the for-bias soft magnetic film 1, alphabet Y a direction of an axis of easy magnetization of the MR film 3, alphabet U a flow direction of the sense current, and alphabet V a direction of a magnetic field generated by the sense current flowing in the MR film 3.
It has been found out, however, that the foregoing conventional structure is unsuitable for the size-reduction of the MR head.
Specifically, when reducing a size of the MR head, a thickness of each of the films 1 to 4 should also be reduced. As a thickness of the MR film 3 is reduced, an electric resistance of the MR film 3 is increased. As a result, unless a magnitude of the sense current flowing in the MR film 3 is suppressed to a lower value, the MR film 3 is subject to rupture or disconnection due to heat generation of the MR film 3 itself and to deterioration of its characteristic due to the generated heat.
On the other hand, when the sense current is lowered, a magnitude of a bias magnetic field generated around the MR film 3 is also lowered. As a result, the for-bias soft magnetic film 1 can not be sufficiently magnetized by such a weak bias magnetic field so that a direction of magnetization of the MR film 3 can not be angularly changed to a direction which is perpendicular to a medium confronting surface 5 of the MR head, resulting in distortion of the reproduced output signal.